1. Field
The subject invention is in the field of apparatus used for making holes in materials, apparatus such as twist drills, fly cutters and hole saws. It is specifically in the field of hole saws having mandrels which are held in the chucks of drill presses, hand held drills and the like.
2. Prior Art
The U.S. patents listed here cover a variety of such hole saws.
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In general hole saws comprise a mandrel, the saw, a dog clutch and a pilot drill. The drill is coaxial with the mandrel and held in place in a hole in the mandrel by a set screw. The saw is a section of tubing with saw teeth at one end and a cap at the other. The cap has a threaded hole at its center whereby the saw can be threaded onto threads on the mandrel until it reaches a shoulder stop. The dog clutch is a collar which fits around and slides axially on a cylindrical surface on the mandrel and is kept from rotating on the mandrel by a key and keyway, mating flats on the mandrel and in the collar hole or the like. Pins extending from one face of the collar engage holes in the cap of the saw when the collar is moved toward the cap and disengage from the holes when the collar is moved away from the cap. When the pins engage the holes, torque is transmitted to the saw from the mandrel via the key and keyway or the like and the pins in the holes in the cap. When the collar is moved away from the cap, disengaging the pins from the holes, the saw can be threaded off the mandrel.
In use, the pilot drill extends beyond the saw and enters the work at the center of the hole to be cut by the saw, the saw teeth cut a cylindrical slit through the material and the cylindrical piece of material cut is called a plug and remains in the saw when the saw is removed from the work.
Removing the plug from the saw is generally not easy and can often be difficult. In any case, it often takes more time to remove the plug than it does to saw the hole, thereby seriously degrading the cost effectiveness and convenience of using holesaws.
It is the prime objective of the subject invention to provide a holesaw incoporating features which facilitate the removal of the plug from the saw. Further objectives are that incorporation of these features will not significantly increase the cost of the holesaw nor degrade its durability.